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Showing 1 to 20 of 23 for “"cristobalite"”.
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Effects of solid solution on the high-low inversion of cristobalite and the stabilization of high cristobalite
The inversion temperature of cristobalite was investigated by incorporating TiO₂, AlPO₄, and BPO₄ into the cristobalite phase using solid state reactions. The combination of TiO₂ and AlPO₄ proved to be most effective in lowering the inversion temperature of cristobalite. Phase diagrams at the high …
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Diversity of compressional mechanisms among SiO2 polymorphs : case of coesite and cristobalite
… of two important silica minerals, coesite and cristobalite. Both of them are framework silicates comprised of fully polymerized corner sharing SiO4 tetrahedra. Coesite, thermodynamically stable above ca. 2.5 GPa and at temperatures in excess of 500 °C, hereafter referred to as coesite-I, is the …
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Diversity of compressional mechanisms among SiO<sub>2</sub> polymorphs : case of coesite and cristobalite.
… of two important silica minerals, coesite and cristobalite. Both of them are framework silicates comprised of fully polymerized corner sharing SiO<sub>4</sub> tetrahedra. Coesite, thermodynamically stable above ca. 2.5 GPa and at temperatures in excess of 500 °C, hereafter referred to as …
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Nuclear magnetic resonance investigations of structural phase transitions in silicon dioxide cristobalite and tridymite and related phases
… phase transitions (SPT's) of the SiO$\sb2$ cristobalite and SiO$\sb2$ and AlPO$\sb4$ tridymite polymorphs. The structural properties and SPT's of these phases have been of mineralogical, physical and industrial interest for decades. However, the microscopic characteristics of the SPT's and …
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Calculations of the elastic constants of crystals as functions of pressure with applications to quartz and cristobalite
… calculations were completed for both quartz and cristobalite using the potentials derived by Lasaga and Gibbs (1987, 1988), Tsuneyuki et al. (1988), van Beest et al. (1990) and Boisen and Gibbs (1993). Among the four theoretical potentials derived from force fields calculated for molecule …
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Investigation of structural phase transitions in minerals and analogue systems by high-temperature magic-angle-spinning nuclear magnetic resonance spectroscopy
… Sr$\sb2$SiO$\sb4$, and AlPO$\sb4$-cristobalite) via high-resolution nuclear magnetic resonance spectroscopy using mostly magic-angle spinning (MAS) techniques. The results provide important insight into each of these SPT's and illustrate the types of information that can be obtained …
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Molecular dynamics simulation of penetrant transport in composite poly (4-methyl-2-pentyne) and nanoparticles of different types
… to allow penetrants to pass through, while in cristobalite silica, the Si and O atoms are densely packed and there are no pores that penetrants can pass through. The transport properties of penetrants in the composite of PMP and nanoparticles of these two types of silica are therefore …
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The approach to equilibrium of mixtures of CaO, A1₂O₃, and SiO₂ heated to various temperatures
… certain compositions of the anorthite-mullite-cristobalite and the anorthite-gehlenite-corundum compatibility triangles were fired to 1400° C. The effect on equilibrium of different raw materials used to form the compositions was also studied. Based on the results of the present investigation …
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Librational displacements of silicate tetrahedra in response to temperature and pressure
… Structural and volume compressibility data for α-cristobalite were determined by single crystal X-ray diffraction methods for pressures up to ~1.6 GPa, where cristobalite undergoes a reversible phase transition. The bulk modulus was determined to be 11.5(7) GPa with a pressure derivative of 9(2). …
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Dynamic Properties of Materials: Phonons from Neutron Scattering
… controversy over dynamic disorder in $\beta$-cristobalite is resolved using this technique. Inelastic neutron spectroscopy (INS) allows \emph{direct} study of vibrational modes through their interaction with the neutron beam, and is the experimental basis for the second strand of the new …
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Materials Characterization and Spectroscopy for a Methane Abatement Catalyst
… transformation into a nonporous quartz-mullite-cristobalite mixture. This suggests indefinite catalyst stability at the former temperature and progressive catalyst degradation at the latter temperature, providing plausible long-term operation conditions and peak temporary conditions for this …
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Durability testing of ceramic candle filters in pressurized-fluidized bed combustion environments
… as low as 700°C. The expansive and destructive cristobalite phase developed in the SiC filters after most of the treatments. The cordierite candle filter showed a decrease in crushing strength associated with grain growth after each high temperature exposure but few other signs of deterioration …
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Molecular Dynamics Simulations of Structural Transitions in Crystalline and Amorphous Inorganic Compounds
… discovered the structure of high-density C-III cristobalite (a phase that has been known to exist but was never indexed), (iii) revealed a ubiquitous tendency for oxygen ordering in various high-density crystalline phases of silica, and (iv) used the knowledge gained concerning structural …
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Studies of clay minerals and their decomposition products
… such phases as spinel, hematite, enstatite, cristobalite and mullite. Illite and montmorillonite started to melt between 1200 and 1300°C, producing a silicate glass that contained Fe(3+) and Fe(2+) ions. Ortho-pnstatite, clino-enstatite and proto-enstatite were identified in the thermal …
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A Mineralogical and Geochemical Assessment of the Potential Respiratory Health Hazard of Ash from Sakurajima Volcano, Japan.
… respiratory diseases. In general ~7 wt. % cristobalite was found, but no other silica polymorphs were observed. SEM imaging showed no fibrous particles that could cause symptoms similar to asbestos. Surface tests showed that the ash did not produce significant amounts of damaging hydroxyl …
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Infrared Spectra Analysis of Thermally Altered Iron Phyllosilicates and the Implications for Mars
… hematite and a high-temperature silica, such as cristobalite. Hisingerite exhibits the same behavior, but its basic spectra structure is retained in the 710°C sample. The near-infrared spectra were compared with spectra from different locations on Mars, collected by both Mars Express and the Mars …
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Degradation and Failure Analysis of Environmental Barrier Coatings under Adverse Operating Environment: Multi-Physics Modelling
… accounted for the β-α phase transformation of cristobalite TGO between 220°C and 270°C, which introduces significant volumetric changes during cooling. Based on the evaluated local stress evolution and distribution in the EBC system during thermal cycles in water-vapor environments, the …
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High-Resolution Multinuclear Magnetic Resonance of Inorganic Solids. Oxygen-17 Nuclear Magnetic Resonance Studies of Inorganic Oxides, Oxyanions, and Silicates
… site. The spectrum of static Si('17)O(,2) (cristobalite) indicates an oxygen-17 e('2)qQ/h = 5.8 MHz with an asymmetry parameter of 0. Because of this VASS NMR is more effective than MASS NMR in line narrowing. In the SiO(,4)('2-) unit of forsterite, each nonequivalent oxygen is partially …
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Studies of the formation of homogeneous mixed silicon-titanium/zirconium oxides by the sol-gel route
… 1100°C, resulted in tetragonal zirconia and some cristobalite being formed. Crystallite sizes have been calculated as being between 2.7 and 1.6nm for tetragonal zirconia and from 4.1 to 2.8nm for cristobalite. Increasing the levels of titania/zirconia in the sample resulted in higher relative …
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Experimental and Modeling Studies of the Methane Steam Reforming Reaction at High Pressure in a Ceramic Membrane Reactor
… structure of glass as a disordered form of cristobalite. The experimental studies of the steam reforming of methane were examined at various temperatures (773-923 K) and pressures (1-20 atm) with a commercial Ni/MgAl2O4 catalyst in a hydrogen selective silica-alumina membrane reactor and …
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